1. Field
The present invention relates to liquid filtration systems and more particularly to such systems that are housed within tanks and are designed to eliminate stagnation that often occurs in the base of the tank.
2. Prior Art
Most prior art liquid filtration systems include a closed tank with an outer skin or shell that is used to house the filtrations system. Such filtration systems are often used to clean the water used in swimming pools. The tanks are typically cylindrical with rounded, rather than flat, ends. The rounded ends allow less material to be used in the tank wall to withstand the pressure in the tank. The tanks may be positioned vertically with a rounded end being located at the bottom of the tank or the tank may be positioned horizontally where it will still have a rounded bottom.
Within the tank, immediately above the round bottom, is a header which generally runs from the front towards the back of the tank. At the front of the tank is a flange that is connected to the tank to provide a through connection for the header to the outside of the tank. Fanning out from the side of the header within the tank are horizontally positioned lateral pipes (laterals) which have thin slots on their sides. These slots let water pass in and out of the laterals but will not let the tank's filtration media, such as sand, enter the pipes. The ends of the laterals away from the header are typically capped.
During a backwash cycle, used to clean the filtration media, water is pumped into the header under pressure, where it is distributed to the laterals, and forced out through the thin slots in the laterals into the media to dislodge and wash away the contamination contained in the media.
Unfortunately, the water used for back washing passes upward through the media from the laterals. The area below the laterals is left stagnant and can permit the growth of bacteria. Deaths have been reported due to bacterial infection which was found to be harbored in the stagnant area of a tank used in the filtration system of a swimming pool.
The importance of eliminating the stagnant areas in filters is illustrated by a news release presented by the British Gardian dated Jan. 05, 2004. Four men on a cruise ship to Bermuda all fell ill. When back on shore, all had a fever so fierce that one received brain damage and another died. The source of the fever was bacteria which grew in a hot tub filter. Punitive damages were seven million dollars. This problem exists in many currently used filters and is obviously an extremely important health matter.
The reason the laterals of the first array are generally not positioned lower in the tank in the rounded base of the tank is that laterals of a length that could be accommodated in an area above the tank base cannot be accommodated in the base tank because of interference with the rounded wall of the tank. Using shorter laterals is not a good option as it reduces the filtration area provided by the laterals and therefore reduced the performance rating of the filtration system.
Prior art attempts to solve this problem did included reducing the lengths of the laterals of the first array so that they could fit into the base of a tank. However, this had the obvious short coming of reducing the effective area of the laterals and thus reduces the filtration capability of the system.
Another prior art approach was to pour concrete into the rounded area to fill it. This technique was abandoned about 30 years ago and filter material such as sand was used to fill this area. Unfortunately, dangerous bacteria can and does grow in this area when filter material such as sand is used as fill.
Yet another prior art approach is to build a floor in the tank immediately below the lateral in the fist array. The floor covers the round stagnation area and thereby eliminates the area in which bacteria would normally grow. A major problem with this approach is the floor is flat and must withstand great pressure. It has to be much thicker than the rounded tank walls to withstand the pressure within the tank. Building this floor is a cumbersome and costly process.
The present invention provides a system which backwashes the stagnant area simply, completely and at low in cost, and at the same time increases the filtration capability of the system. It uses only standard plumbing parts and is easily fabricated at low cost.